Faculty Publications
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Item Studies on concrete cylinders subjected to elevated temperatures(2010) Babu Narayan, K.S.; Anil Kumar, G.; Chandrakala, C.; Shashikumar, H.M.; Venkataramana, K.; Yaragal, S.C.; Chinnagiri Gowda, H.C.; Reddy, G.R.; Sharma, A.Concrete is a poor conductor of heat, but can suffer considerable damage when exposed to fire. Concrete in structures is likely to be exposed to high temperatures during fire. The relative properties of concrete after such an exposure are of great importance in terms of the serviceability of buildings. Unraveling the heating history of concrete is important to forensic research or to determine whether a fire exposed concrete structures and its components are still structurally sound or not. Assessment of fire damage concrete structures usually starts with visual observation of color change, cracking and spalling. On heating, a change in color from normal to pink is often observed and this is useful since it coincides with the onset of significant loss of concrete strength. This work reports the characteristics of concrete at elevated temperatures. Popular normal strength grades (M20, M25, M30, M35, M40 and M45) produced by Ready Mix Concrete (RMC) India, Mangalore have been used in production of test specimens (150 mm diameter and 300mm height cylinders) to obtain more meaningful and realistic data. In the preliminary phase 150 mm diameter and 300mm height cylinders were cast, cured and tested by destructive method for gathering data on strength characteristics. Later these test samples were subjected to elevated temperatures ranging from 100°C to 800°C, in steps of 100°C with a retention period of 2 hours. After exposure, weight losses were determined and then again destructive tests were conducted to estimate the residual split tensile strength. Test results indicated that weight and strength significantly reduces with an increase in temperature. © 2010 CAFET-INNOVA TECHNICAL SOCIETY. All rights reserved.Item Strength characteristics of concrete exposed to elevated temperatures and cooled under different regimes(2012) Yaragal, S.C.; Babu Narayan, K.S.; Adari, S.Concrete loses strength in the event of accidental fires. The residual strength of normal strength concrete is of vital importance for ascertaining serviceability of buildings after the event of fires. Strength loss in concrete is dependent on the temperature of exposure, its duration and the way it gets cooled. In this study concrete cubes of size 100 mm have been cast for M25 grade of concrete, 28 days water cured. The specimens were subjected to elevated temperatures of 150°C, 250°C, 350°C, 450°C and 550°C with a retention period of 1 hour. After 1 hour of exposure, specimens were allowed to cool under different cooling regimes to ambient temperature. Later their appearance, colour and cracks were observed and also weight losses were determined. Further, destructive tests were conducted to estimate residual compressive and split tensile strengths. Important performance changes have been presented and discussed. Split tensile strengths are related to compressive strengths for all the cases of cooling regimes.Item Goubau line based end-fire antenna(John Wiley and Sons Inc. P.O.Box 18667 Newark NJ 07191-8667, 2019) Rudramuni, K.; Tharehalli Rajanna, P.K.T.; Kandaswamy, K.; Majumder, B.; Zhang, Q.This article proposes a simple and low profile planar Goubau line based end-fire antenna. End-fire radiation is achieved by modifying the Goubau line into inverted periodic arrangement of V-shaped unit cells. Designed prototype is simulated and verified experimentally. Both the simulated and measured results are in good agreement. Proposed antenna radiates toward end-fire direction between 7.8 and 8.3 GHz. The maximum gain of the antenna is obtained around 7.2 dBi. The average efficiency is observed 70% over the entire operating bandwidth. Proposed end-fire antenna has a single metallic layer with simple configuration which is easy to fabricate and also easy to integrate with other electronics circuits. The proposed antenna can be used for satellite and RADAR applications. © 2019 Wiley Periodicals, Inc.Item Evaluating the effects of forest fire on water balance using fire susceptibility maps(Elsevier B.V., 2020) Venkatesh, K.; Konkathi, K.; Ramesh, H.Sudden and long term changes in the landscape can be attributed to periodic wildfires which, is a cyclic occurrence at Kudremukh national forest in Western Ghats of India. These land-use changes influence the hydrology of landscape, causing disintegration of soil, loss of biodiversity, changes in stream and flooding. To understand and account for these land-use changes, a new approach was implemented by developing fire susceptibility map from topographic, climatic and human-induced factors and validating it with MODIS (Moderate-resolution Imaging Spectro-radiometer) fire points for discretising accuracy. The fire susceptibility map can be used for studying the long-term (year or more) effects of fire on water balance systems. The fire susceptibility map generated for the years 2005 and 2017 was overlaid with MODIS LULC (Land Use Land Cover) for establishing the post-fire scenario whereas MODIS LULC MCD12Q1 (2005 and 2017) was considered as the no-fire scenario to analyse the intensity of the fire and its effect on streamflow and infiltration. These maps along with historical satellite hydro-climatic datasets, were used to assess the effect of forest fire on hydrological parameters using the SWAT (Soil and Water Assessment Tool) model. No-fire and post-fire conditions were established by modifying SCS-CN (Soil Conservation Service-Curve Number) based on previous works of literature to represent the catchment as unburnt and burnt area. The SWAT model was calibrated (2002–2008) and validated (2009–2012) for establishing a baseline scenario. The sensitive parameters obtained from SUFI-2 (Sequential Uncertainty Fitting) algorithm in SWAT-CUP (Calibration and Uncertainty Programs) were used to simulate stream flows till 2017 due to lack of observed streamflow data for the year 2017. It was inferred that the effect of wildfire on flows in recent years (2017) had increased radically when compared to the flows before a decade (2005), diminishing the rate of infiltration and causing the deficit in groundwater to energise. The methodology can further be executed in any forest area for distinguishing fire hazard zones and implementing prior actions in those areas for mitigation of forest fires and maintaining sustainable water balance. © 2019 Elsevier LtdItem Satellite-based top-down Lagrangian approach to quantify aerosol emissions over California(John Wiley and Sons Ltd vgorayska@wiley.com Southern Gate Chichester, West Sussex PO19 8SQ, 2020) Nizar, S.; Dodamani, B.M.Accurate forecasting of air quality demands better estimates of aerosol emissions. The accuracy of conventional bottom-up approaches to estimate aerosol emissions depends on the degree to which various influencing parameters are estimated. The availability of satellite observations not only enhances the capability of determining various influencing parameters, but also provides alternate ways of assessing aerosol sources. The present study employs a Lagrangian approach to the Advection Diffusion Equation (ADE) to estimate the transported aerosols and hence the Aerosol Source Strength (ASS) using satellite-measured Aerosol Optical Depth (AOD) and reanalysis wind data. This top-down approach is based on the advection and diffusion of atmospheric aerosols considering wind circulation and atmospheric conditions rather than using indicative parameters. ASS was computed every 3 hr at a 0.25°×0.25° grid across California during July 2018. For the computation, AOD retrievals were obtained from the Geostationary Operational Environmental Satellite (GOES)-16 with observations every 15 min. The data were resampled to the grid every 3 hr, and backward trajectories were run at every gridpoint to ascertain the initial aerosol concentration for the ADE. The final aerosol concentrations obtained from the ADE model were then compared with the observed AOD to obtain the ASS during that time period. The results are indicative of higher ASS around wildfire locations. The ASS values also show good correlation (R2=0.886) with Fire Radiative Power (FRP) obtained from Terra MODIS fire product. The method was further applied to investigate the spatial correlation of ASS with power plant density, which reveals a steady increase in ASS with power plant density (R2=0.82). © 2020 Royal Meteorological SocietyItem Simplified Method to Predict Residual Strength of Reinforced Concrete Columns Under Natural Fire Conditions(Springer, 2024) Akkannavar, C.; Prashanth, M.H.; Joshi, C.Studies on the Reinforced Concrete (RC) columns under natural fire conditions are critical since the failure of columns leads to progressive failure of the building. Many experimental and analytical studies have been conducted to investigate the columns under fire conditions. Most studies have investigated fire conditions by utilizing standard time–temperature relationships such as ISO-834, ASTEM E119, and other nominal fire curves. This paper presents a simplified method to evaluate the axial capacity of RC columns subjected to natural or realistic fires. A parametric natural fire model is developed from EN.1991.1.2.2002 guidelines, considering important parameters into account to define the natural fire curve. Thermal analysis is carried out using the finite element software SAFIR to determine the temperature distribution within the column’s cross-section. The mechanical properties of concrete and steel change with an increase in temperature. The reduction factors for the compressive strength of concrete and the yield strength of steel at elevated temperatures are derived from Eurocodes. Using updated temperature-dependent strength parameters for concrete and steel, the capacity of a column is estimated. The proposed methodology can be used to estimate the residual strength of RC columns for realistic fire situations. © The Institution of Engineers (India) 2024.Item Residual strength estimation of RC columns subjected to elevated temperatures from stress block parameters(Emerald Publishing, 2025) Akkannavar, C.S.; Prashanth, M.H.Purpose: In structural fire engineering, the design of columns is done either by prescriptive approaches or by empirical equations derived from experimental research. Performance-based design is the emerging methodology for designing structures under fire, which is case-specific. There is a need to develop design equations from first principles to design/find the residual strength of the column at elevated temperatures. The present study aims to develop equations from stress block parameters to find the residual strength of reinforced concrete (RC) columns subjected to elevated temperatures. Design/methodology/approach: The stress-strain variation across the cross-section of the RC column is determined at elevated temperatures. Based on the updated stress distribution diagram, stress block parameters are derived for various depths of neutral axis (NA) and different temperatures. Using updated stress block parameters, Pu-Mu interaction curves are generated for elevated temperatures. The results are verified against conventional methods and experimental results. Findings: The load-carrying capacity calculated from the proposed methodology is analogous to the experimental results. The methodology can be utilized to estimate the residual strength of RC columns subjected to elevated temperatures. Originality/value: The work done here attempts to develop the equations to estimate the residual strength of the column. The work involves calculating the strength of columns subjected to fire curves. © 2024, Emerald Publishing Limited.